At present, there are in the market thousands of different types of powered steering gearboxes. Most of them, and those most broadly applied by the automotive industry, are powered steering gearboxes including an assistance pump that energizes the hydraulic circuit in charge of assisting the rack bar and pinion gearbox mechanism of the steering gearbox.
This kind of assistance has the inconvenience that the pump is permanently connected while the vehicle is running, either when it circulates at 10 m/h or 150 m/h. It is already known in the automotive industry that steering gearboxes require such assistance only when the vehicle requires maneuvering at low speed, while at high speed the power steering mechanisms are practically inactive. However, the assistance pump continues working, consuming unnecessary energy from the engine which, depending on the case, may range about 4–5 HP.
It is an object of the present invention for a fluid flow control device for controlling the assistance fluid circuit. The fluid may be directed to the hydraulic pump or to the fluid reservoir depending on the speed at which the vehicle is running. When the vehicle circulates under certain parameters, for example at high speed, the hydraulic assistance is not necessary, so the fluid is directed to the reservoir, and when the vehicle is stopped or running at a low speed the fluid is directed to the pump for assisting the steering mechanism. This allows the pump to work in vacuum when the vehicle circulates at high speed, (avoiding impelling a pump unnecessarily), reducing the engine wearing and fuel consumption.
There are several control mechanisms for controlling the steering assistance depending on the working conditions of the engine. For example, U.S. Pat. No. 5,740,880 of Miller et al, discloses electric motors having controllable induced armature fields, such as induction motors and synchronous reluctance motors, used in power assisted steering systems for motor vehicles. Tailoring induced armature fields conserves power or rotor flux in accordance with the speeds of motor vehicles including the power assisted steering system. In particular, one or more flux programs or maps are provided for the power assisted steering system with the flux map or program being accessed or addressed by means of the vehicle speed. During low speed operation of the motor vehicle, for example to perform parking maneuvers where speeds are near zero and steering forces are near or at maximum, the rotor flux is programmed to maximum. For high speed operation, such as highway and rural motor vehicle operation, the rotor flux is programmed to a low value so that internal loss mechanisms in the power assist motor and motor controller are minimized yet provide sufficient rotor flux to meet steering needs such as lane changes, obstacle avoidance and the like. Various transition speeds and flux transition curves provide smooth transitions between high flux levels and low flux levels.
This solution can be applied to an electric steering gearbox, but cannot be applied to a hydraulic gearbox, since it is not possible to control pump pressure, like the value of current in the present case.
U.S. Pat. No. 5,794,736 is referred to a fluid control system for a vehicle power steering mechanism having a manually driven steering member and a fluid driven driving member operatively connected to steering means of the vehicle by which steerage of the vehicle is achieved, the system including a first valve for metering pressurized fluid flow to the fluid operated driving member in response to the force required to move the steering means when operating the manually driven steering member, the first valve including at least two independent metering valve means each of which are simultaneously operated by the steering member to meter fluid flow to and/or from the fluid operated driving member at a predefined rate, at least one of the metering valve means communicating independently to a drain via a second valve being arranged to selectively connect and disconnect said at least one of said valve means to the drain in response to vehicle speed.
All these mechanisms tend to regulate the fluid pressure by acting on the fluid pump or regulating flow through valves, in order to maximize circuit power when the vehicle is stopped or running at a very low speed and minimize it at high speed.
None of the well-known means leaves the pump working in vacuum depending on the vehicle working conditions, as the present invention does.